I find the lumia GUI quite ugly.
Everything displayed takes so much space, like that you can only see 4 contacts at a time. The user has actually to scroll all the time to gather the same amount of informations he could catch on the N9 or comparable devices with one view.
Plus, even though it's smooth, it's rather slow - e.g. hold the Lumia next to your N9 or Symbian phone and open the contacts. While on the Nokias, the contacts will appear instantly, you will have to wait for the animations to finish on the Microsoft Lumia first.
And, what bothers me most is that there is no free access to the device, the only way to sync contacts is through hotmail or exchange and the only way to instal apps is through the Microsoft market, which is not only the smallest compared to apple, Android and ovi, but also the most expensive one.
I cannot recommend windows phone at all!